1. Field of the Invention
The present invention relates to a dielectric filter including a dielectric resonator.
2. Description of the Related Art
The standardization of fifth-generation mobile communication systems (hereinafter referred to as 5G) is currently ongoing. For 5G, the use of frequency bands of 10 GHz or higher, particularly millimeter wavebands of 30 to 300 GHz, is being studied to expand the frequency band.
Among electronic components for use in communication devices are filters including resonators, such as band-pass filters. Dielectric filters including dielectric resonators are promising as filters usable in the frequency bands of 10 GHz or higher.
In general, a dielectric filter includes: a resonator body formed of a dielectric material; a surrounding dielectric portion formed of a dielectric material having a relative permittivity lower than that of the dielectric material used to form the resonator body; and an input/output conductor portion. The surrounding dielectric portion is present around the resonator body. The input/output conductor portion is used for at least one of supply of an electromagnetic wave to the resonator body and reception of an electromagnetic wave from the resonator body. Such a dielectric filter is described in, for example, JP 2006-238027A, JP H11-355005A, and JP H5-304401A.
JP 2006-238027A describes a dielectric filter including a dielectric substrate, a plurality of dielectric resonators embedded in the dielectric substrate, an input portion, and an output portion. Each of the dielectric resonators of this dielectric filter is in a cylindrical shape. The dielectric resonators are arranged with a predetermined spacing between adjacent ones along the direction of signal transmission in such a posture that the direction of axis of each dielectric resonator is perpendicular to the direction of signal transmission. The input portion and the output portion are provided inside the dielectric substrate, and drawn out to the external surfaces of the dielectric substrate. The input portion is located near one of the dielectric resonators so as to be aligned with this dielectric resonator in the direction of signal transmission. The output portion is located near another one of the dielectric resonators so as to be aligned with this dielectric resonator in the direction of signal transmission. The dielectric resonators and the dielectric substrate in JP 2006-238027A respectively correspond to the resonator body and the surrounding dielectric portion mentioned above. Both of the input portion and the output portion in JP 2006-238027A correspond to the input/output conductor portion mentioned above.
JP H11-355005A describes a filter including two dielectric substrates, a plurality of dielectric resonators, two microstrip lines, and a grounded conductor. In this filter, the two dielectric substrates are disposed on the top and bottom of the grounded conductor to sandwich the grounded conductor. In the dielectric substrate on the top side, a plurality of holes are formed to open at the top surface of the dielectric substrate. The dielectric resonators are embedded into the holes. The two microstrip lines are formed on the top surface of the dielectric substrate on the top side. One of the microstrip lines is located near one of the dielectric resonators. The other of the microstrip lines is located near another one of the dielectric resonators. In the dielectric substrate on the top side, there are formed a plurality of voids each of which is situated between the dielectric resonator and the grounded conductor. The dielectric resonators and the dielectric substrates in JP H11-355005A respectively correspond to the resonator body and the surrounding dielectric portion mentioned above. Both of the two microstrip lines in JP H11-355005A correspond to the input/output conductor portion mentioned above.
JP H5-304401A describes a dielectric filter including two dielectric resonators, a resin embedding the two dielectric resonators, thin-film electrodes covering the resin, and two input/output pins. The dielectric resonators and the resin in JP H5-304401A respectively correspond to the resonator body and the surrounding dielectric portion mentioned above. Both of the two input/output pins in JP H5-304401A correspond to the input/output conductor portion mentioned above.
In mobile communications, traffic has been increasing in recent years. To deal with this problem, the allocation of wide useful frequency bands is important, as well as an increase in communication speed. When wide useful frequency bands are allocated to communication systems such as 5G in frequency bands of 10 GHz or higher, filters having large fractional bandwidths are required as filters to be used in the communication systems.
However, increasing fractional bandwidths is difficult for conventional dielectric filters.